Plasma sputtering processes are extensively used in the semiconductor, flat panel, data storage, hard coating and industrial glass coating industries. In a sputtering process atoms of a material are liberated from a target material and deposited onto a substrate. In a reactive sputtering process, alternatively, atoms of a material are liberated from a target material allowing the atoms to react with a gas to form a coating that is, subsequently, deposited onto a substrate. In the semiconductor industry a reactive sputtering process may be employed, for example, to deposit a dielectric insulating layer (such as, silicon nitride) onto a silicon wafer. In the hard coating industry, a reactive sputtering process may be used, for example, to deposit a wear-resistant layer (such as, titanium nitride) on a mechanical part.
Sputtering is a vacuum deposition process in which a sputtering target is bombarded with ions, typically an ionized noble gas, and momentum transfer mechanically frees the atoms of the target material. The target material then coats a nearby substrate.
In a reactive sputtering process a reactive gas is introduced into the sputtering chamber and the atoms of the freed target material react with the reactive gas to form a coating material. For example, the target material can be aluminum and the reactive gas can be oxygen, the combination of which produces a coating of aluminum oxide. In another example, carbonaceous gas (such as, acetylene) can be used as the reactive gas to produce coatings such as silicon carbide and tungsten carbide by combining the acetylene with silicon and tungsten targets, respectively. The conductive atoms of freed target material react with the reactive gas in a plasma in the sputtering chamber to produce the compound (coating material) that coats the substrate.
Proper control of sputtering process parameters (such as, voltage and current supplied to the plasma chamber by a power generator) is important to ensure that adequate sputtering quality and system throughput is achieved. Sputtering system faults (such as, warning or error signals) may occur during operation. These faults are indicative of problems in the sputtering process or the onset of problems that may have adverse effects on the sputtering process. One such fault occurs when the power generator of a sputtering system outputs a voltage that is below a specified threshold; this condition can result in fewer or zero atoms of target material being freed from the target. Further, another such fault occurs when the power generator outputs a current density to the plasma chamber above a specified threshold value; this condition can result in arcing and subsequent termination of the sputtering process due to the presence of the arcing.
Control systems for conventional sputtering systems react to the occurrence of individual faults. Multiple faults, however, may occur within a short period of time during the operation of the sputtering system. A control system's reaction to each of the individual faults may not be optimum where there are multiple faults.
A fault handling system and methods for controlling the operation of a power generator of a sputtering system in the presence of multiple sputtering system faults are therefore needed.